Heres an excerpt:
"Melaleuca is a harsh antiseptic used to repair torn fins and aid in healing sores. Unfortunately, it is an irritant that seems to have an adverse effect on certain fish. Most fish can handle melaleuca just fine, this includes most "scaleless" fishes as well. So far, the fish that seem to have problems with melaleuca are anabantoids and pencilfish. Since it is an irritant, it is not unlike using alcohol or peroxide on a cut or a scrape. The melaleuca irritates the cells to speed the healing process. With most fish this would be fine and it wouldn't harm the fish in any way, but labyrinth breathers are different. Their labyrinth organs are sensitive to the melaleuca and with a full dose of Melafix, you can kill a betta or a gourami within a few days. The labyrinth organ is the most important organ in a betta's body, that is it's lung. Like humans, if an irritative chemical gets into our lungs, we will have adverse problems from it, possibly even death, the same goes for bettas with a dose of straight Melafix."
From http://www.aquaria.info/index.php?na...=17002&start=0

That makes sense. I can say that I used the medication successfully on both betta splendens and dwarf gouramis with success. I can see how an overdose of the medication (or if the medication was used in a container with a narrow opening, such as a full fish bowl) then the oil might collect at the surface. A surfacing betta going for air could then, feasibly, get some in its labyrinth organ.

I'm going to stick to my guns to some extent, though. As long as you dose properly (thus disallowing surface buildup) and have a decent amount of surface agitation, you're probably in the clear.

Personally, I'd rather take my chances with a medication that I have had success with in treating fin rot, even with the risks involved. I've seen fin rot kill a guppy in three days' time, so I think it's worth the risks.

The bottle of bettafix says to add the stuff for 7 days in a row, then change the water (at least I think thats what it says. I misplaced my bottle). If you use it, how much should you put in a gallon bowl?